Metal vaporization crucible with upstanding walls for confining and condensing vapor



MTRM- Dec. 3, 1968 FOR CONF Origi L Y L 50$ W D/d N L f I A/M United States Patent ABSTRACT OF THE DISCLOSURE A QQlCilLlQfOl' holding molten metal, provided with a wall around the rnetal bathand extending upwardly therefrom to confinuapor ascending from the bath surface and condense appr not moving directly toward the material above the bathttobecoated by condensation thereon. Metal condensed on the wall runs down back into the bath.

This is a continuation of my application Se'r. No. 482,193, filed Aug. 24, 1965, now abandoned.

This invention relates to a cr ugibl eifnrathqlgpggizqliml. of metal. In particular, the invention concerns a crucible ha vingia confining structure formed by a wall extending upwardly therefrom. This structure serves to confine the volyjng' vapor and affords a surface for the condensation e oFsuelf'po'rtioh of the vapor cloud as may tend to have a random direction and to depart from the desired course of travel.

In the generation of metal vapor, as for example, in apparatus for the coating of sheet material by the condensation of metal vapor thereon in a vacuum, it is desirable that the metal vapor travel from the source, usually a top-heated boiling bath of molten metal, directly to the substrate to be coated. -It is inevitable, however, that some substantial portion of the ascending vapor cloud will have a random direction of travel and will impinge and condense on some part of the coating apparatus instead of the substrate. This is objectionable not only because of the loss of metal vapor but, even more importantly, because accumulations of condensed vapor at random locations will, in time, require complete shut-down of the apparatus for clean-out. Downtime directly reduces the possible output of the apparatus and increases the total unit cost of the product.

It is accordingly the object of my invention to provide means for confining the ascending vapor cloud and tending to direct it toward the substrate and, further, to provide such means of a character which will serve to condense vapor not traveling directly toward the substrate and return it to the boiling bath for re-vaporization. My invention contemplates the provision, over a vaporization crucible, of a wall confining the ascending vapor cloud, of such nature that, in the normal operation of the crucible, it will be heated to a temperature above the melting point of the metal being vaporized but below the temperature at which vapor impinging thereon will be immediately reflected by thermal emission. As a result, the random-directed vapor impinging on the confining walls condenses to liquid form and runs downwardly therealong back into the crucible. The remainder of the vapor traversing the desired course, continues thereon untlil it condenses on the substrate traveling above the wa l.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. in the drawings:

3,414,251 Patented Dec. 3, 1968 "ice FIGURE 1 is a plan view of metal-vaporization apparatus incorporating my invention; and

FIGURE 2 is a section therethrough taken along the plane of line IIII of FIGURE 1 and showing the relalive path of the substrate traveling over the crucible.

Referring in detail to the drawings, a crucible 10 may be conveniently composed of a metal receptacle 11 having a lining 12 of a re gtory material which is not significantly attacked by molten aluminum, e.g., boron nitride. A charge of metal 13, such as aluminum, in the crucible 10 is adapted to be melted and vaporized by top heating. In the example illustrated, heating is effected by electron bombardment. A source of electrons is afforded by an electron-beam ,gun 14 extending alongside crucible 10 and maintained at a high, (i.e. several thousand volts) negative potential relative thereto.

A side wall 15, generally similar in outline to the crucible, extends upwardly from the edges thereof. The side wall is provided with an entry port 16 for a beam of electrons from gun 14. Means (not shown) whereby they traverse a curved path, such as a direct current magnetic field, are provided, so they ultimately impinge on the top of charge 13. A ring 17 restricts the beam for entry into port 16 with a minimum of bombardment of the edge thereof.

Wall 15 has a lining 18 of a material resistant to the effect of contact by metal vapor, e.g., aluminum vapor, from crucible 10. This material may be alumina, boron nitride, aluminum nitride, zirconia or silicon nitride, or a mixture thereof. Wall 15 may be composed entirely of such material but usually a lining thereof having a thickness of the order of .010 or .015" will sufiice. The lining is applied over a backing of thermal insulating material of any suitable character.

A substrate 19 to be coated with metal is conducted across the top of wall 15 by any convenient means not shown and, of course, the entire apparatus shown is en- 1 closed in a v acuum chamber which is pumped down to a suitable low pr =:su"r'such as 1 micron of mercury or lower. M It will be evident that metal vapor boiling off the surface of the molten charge 13 will form an ascending cloud most of which will eventually reach substrate 19 and condense thereon to form a coating on the lower surface thereof. Some of the vapor will, however, condense on the interior of wall 15, or, more specifically, on lining 18. Such portion will remain liquid because of heat radiated from charge 13 and because of the heat of vaporization liberated when the vapor condenses, and when collected into globules of sufiicient size, will run down side wall 15 and back into charge 13 for further heating therein and re-vaporization therefrom. The side wall is made of a Qfick, heat insulating material and may be further surrounded by a radianeheat shield, 'not'shown, so as to retain as much as possible of the radiant heat and heat of condensation to assure that the condensate does not solidify and build up but returns to the crucible as liquid. ide w all l5 th'us acts in two ways, first it generally confiffs the vapor in an upward path toward tlfe substrate and second, it serves as a condenser for apor which because of its directln 61 6 i substrate in any event. As a result, a large part of the vapor actually reaches the substrate and that which does not is promptly returned to the crucible in liquid form. The invention obviously improves the efiiciency with which metal is deposited on the substrate, but what is more important, it prevents fouling the adjacent portions of apparatus in the vacuum chamber with an unwanted accumulation of aluminum condensed from the vapor intended for coating.

Although I have disclosed herein the preferred embodiment of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention as set forth in the claims.

I claim:

-in a g letalmam atieawa aalet le.Hil rucibleaadapted .to -containtaacharge. .of,.moltefi:1etal15 l:" m deposit on a substrate spaced above the crucible, and means I91 tgp -l eat ing th e charge to -v n 11.: the combination therewith of a side wall extending arounc? the greater portion of the edge'of the crucible, at least, and from the crucible substantially to the substrate enclosing the space above the crucible and confining the vapor but allowing free ascent of vapor from the charge in a generally vertical direction, said wall having its inner .group consisting of alumina zirconia, aluminum nitride, QHELPlU'lde and silicon nitride and bemgTHereby adapted ieaat aenli lil iialimtetiera t Striking it and lface, at least, composed of a material selected from the 15 duct the resulting liquid metal downwardly back into the crucible.

2. Apparatus as defined in claim 1, characterized by said top-heating means being an electron-beam gun adjacent the crucible, said side wall having an opening therein to admit the beam from said gun.

References Cited UNITED STATES PATENTS 2,665,223 1/1954 Clough et a1 117107 3,079,136 2/1963 Soine 26639 3,183,563 5/1965 Smith 1'l7l07 X 3,230,110 1/1966 Smith 1l7-228 J. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

